Sometimes, when Anthony Amore gets frustrated by his 11-year hunt for the Isabella Stewart Gardner Museum’s stolen paintings, he and the FBI agents on the case will talk each other through the ways that other museums’ stolen masterpieces have come home.

If the 13 Gardner artworks swiped in 1990 are ever returned, will it be thanks to an old crook, ready to deal at last? A family member, sorting through inherited bric-a-brac in some long-locked New England attic? Or a tip from the public, someone who sees or hears a final clue?